The overall purpose of these studies is to test the hypothesis that glutamine has a protein anabolic effect in humans. Although Glutamine is the most abundant amino acid in the body, and can be synthesized de novo, muscle free glutamine pool can be depleted with stress and protein wasting diseases, and replenishment of the glutamine stores is associated with improved nitrogen balance in such conditions. These studies will use infusion of stable and radioactive tracers of leucine and glutamine to determine in vivo in healthy humans: 1) whether glutamine stimulates growth hormone secretion; 2) whether an acute decrease in plasma glutamin concentration has a protein catabolic effect; 3) whether enteral glutamine can alter the catabolic response to glucocorticoids; and 4) whether an acute decrease in plasma glutamine concentration enhances the protein catabolic response to glucocorticoids. These studies will expand understanding of the physiologic role of glutamine in protein metabolism and should, if they provide evidence for an anabolic role of glutamine in humans, support the use of enteral or parenteral supplementation as an ineffective, inexpensive means of preserving body protein stores during severe illness.